F-FDG PET/CT for Posttreatment Surveillance Imaging of Patients with Stage III Merkel Cell Carcinoma.

The purpose of this study was to investigate the diagnostic and prognostic value of F-FDG PET/CT for surveillance imaging in patients treated for stage III Merkel cell carcinoma (MCC). This retrospective study included 61 consecutive stage III MCC patients who were clinically asymptomatic and underwent surveillance F-FDG PET/CT. Findings were correlated with either pathology or clinical/imaging follow-up. The median follow-up period was 4.8 y. Statistical analyses were performed. F-FDG PET/CT detected unsuspected recurrences in 33% patients (20/61) with lesion-based sensitivity, specificity, and accuracy of 92%, 93%, and 93%, respectively. The mean ± SD SUV for malignant and benign lesions was 7.5 ± 3.9 and 3.8 ± 2.0, respectively. Unknown distant metastases, as first recurrence site, were noted in 12 of 61 patients. Those with positive disease on F-FDG PET/CT within 1 y of definitive treatment had relatively worse overall survival ( < 0.0001). After adjustment on stage, risk of death increased with a higher SUV (hazard ratio for 1 unit = 1.17; = 0.006) and with a higher number of positive lesions on F-FDG PET/CT (hazard ratio for 1 additional lesion = 1.60; < 0.001). Postdefinitive treatment surveillance F-FDG PET/CT scanning detects unsuspected recurrences and has prognostic value. Inclusion of F-FDG PET/CT within the first 6 mo after definitive treatment would be appropriate for surveillance and early detection of recurrence. Our data merit further studies to evaluate the prognostic implications.